The proposed research is a five-year longitudinal study of 900 high-risk young people first studied as adolescents in 1984-1985. Our objectives are: (1) to assess the degree of change in behaviors that are associated with risk of HIV infection over the ten year course of this project; (2) to determine the association between behavior change and knowledge and attitudes about AIDS in subjects at varying degrees of risk for HIV infection over the longitudinal course of this project; (3) to search for factors that predispose or protect high-risk young people's participation in behaviors that are associated with risk of HIV infection; (4) to determine the extent to which behaviors that have already placed adolescents at high-risk for HIV infection actually result in seropositivity in young adulthood; and (5) to determine changes in behavior, social relationships and cognitive capacities in subjects who become infected with the HIV virus during the course of this study. The study will consist of individual in-person interviews every other year with three groups of the original sample: those at high risk for AIDS; similar youths at moderate risk: and similar youths at lower risk. In addition, a fourth group composed of the most recent sexual partners of those youths who had sex within the last month would be recruited. A component of this grant proposes to study risk factors in the blood samples of the youths. During each reinterview period, the blood samples of the youths. During each reinterview period, the blood samples would be tested for HIV antibodies and other factors that might increase the youth's risk, such as syphilis and Hepatitis B.